Field of Invention
The present invention relates to a cutting tool and, more particularly, to a damper for a cutting tool.
Related Prior Art
Vibration is closely related to our everyday. Pleasant music or annoying nose is caused by vibration.
In many devices, there are a stationary element and a rotational element. For example, in a motor, a shell is a stationary element and a mandrel is a rotational element. In a washing machine, a shell is a stationary element, and a drum is a rotational element. In a cutting operation, a blade is held still and a work-piece is rotated. In another cutting operation, a work-piece is held still and a blade is rotated. There is transfer of energy between the rotational elements and the stationary elements, and vibration occurs. Vibration is characterized by two properties, i.e., frequency and amplitude. Resonation occurs when resonation the natural frequency of vibration is identical to the frequency of stimulation. Resonation causes excessive deformation and failure of a mechanical system.
To suppress vibration, there are dampers. A damper can be used in a stationary element such as a column or a beam of a building to suppress vibration of the building caused by an earthquake. A damper can be used in a movable element such as a drill or blade of a cutting tool to suppress the vibration of the cutting tool in operation.
Japanese Patent Application Publication No. 2003-136301 discloses a cutting tool including a blade attached to a front end of a shank. A deep hole is defined in the shank. The deep hole includes an open end at a rear end of the shank and a closed end near the front end of the deep hole. A damper is inserted in the deep hole, adjacent to the blade. A super hard core is inserted in the deep hole, behind the camper.
Japanese Patent Application Publication No. 1994-31507 discloses a cutting tool including a shank. Viscous fluid and a balancing block are introduced into a deep hole defined in the shank.
Japanese Patent Publication No. 2979823 discloses a helical spring inserted in a deep hole defined in a shank of a cutting tool and a viscous elastic material provided between the helical spring and a closed end of the deep hole. A blade is attached to the helical spring. A frictional, vibration-absorbing material is provided between the blade and the shank for transforming vibration into heat that can be dissipated, thus reducing the vibration.
In each of the foregoing references, it is difficult to make the deep hole in the shank where the external diameter of the shank is small. It requires a deep-hole drill to make the deep hole in the shank, and this is expensive. Moreover, the deep hole compromises the strength of the shank. Moreover, the structure is complicated and entails a high cost.
Japanese Patent Application Publication No. 1994-31505 discloses a shank including a bore defined therein for connecting a damper made of a different material. Friction between the shank and the damper reduces the vibration.
Japanese Patent Application Publication Nos. 2001-96403 and 2003-62703 both disclose a damping material introduced into a bore defined in a shank of a cutting tool. The damping material absorbs the energy of the vibration, thus reducing the vibration. In addition to the foregoing problems, these references involve the use of the damping material including Mn—Cu alloys that are often expensive and cannot be fabricated easily. Therefore, it is difficult to reach a high performance at a low cost according to these references.
Japanese Patent Application Publication No. 2005-177973 is intended to provide a cutting tool with excellent damping at a low cost by making a polygonal pocket in a shank of a cutting tool, inserting a damper in the pocket and closing the pocket with a cover, thus keeping the damper in the pocket. The damper can be strip-like, cylindrical or polygonal. The damper is not connected to the shank, with a gap between them. During an operation of cutting a work piece with the cutting tool, the damper alternatively hits different portions of the wall of the pocket because of inertia, thus reducing vibration. The effect of the reduction of the vibration depends upon the gap. The effect of the reduction of the vibration is poor if the gap is too small or too big. It is however difficult to keep the gap within an appropriate range.
As disclosed in U.S. Pat. No. 8,371,776, a cutting tool 100 includes a blade unit, a shank 20 and a damper 30. The blade unit includes a seat 10 and a blade 12. The seat 10 includes a shank-connecting portion 11 and a blade-connecting portion 14. A thread 13 is formed on the shank-connecting portion 11 of the seat 10. The shank 20 includes a thread 22 formed on the wall of a pocket 21. The damper 30 includes a rod 31, a thread 32 formed on the periphery of the rod 31, and a groove 33 made in an end of the rod 31. The damper 30 is inserted in the pocket 21 before the thread 13 is engaged with the thread 22 so that the damper 30 is kept in the pocket 21. There is another gap between another end of the damper 30 and the shank-connecting portion 11. There is a gap between an end of the damper 30 and a closed end of the pocket 21. There is a gap between the threads 32 and 22. The effect of this damper 30 is however unsatisfactory.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in prior art.